Make MathBigInset working

Make MathBigInset working
        * src/cursor.C
        (LCursor::plainInsert): combine the previous math atom with the new
        one to a MathBigInset if possible

        * src/mathed/math_biginset.[Ch]
        (MathBigInset::name): implement
        (MathBigInset::isBigInsetDelim): new, test whether a given token is
        a valid MathBigInset delimiter

        * src/mathed/math_biginset.C
        (MathBigInset::size): handle Big, Bigg and Biggg
        (MathBigInset::increase): ditto
        (MathBigInset::draw): fix deco drawing
        (MathBigInset::write): append space if necessary

        * src/mathed/math_factory.C
        (createMathInset): handle l->inset == "big"

        * src/mathed/math_parser.C
        (Token::asInput): return a token as input, stolen from tex2lyx
        (void Parser::parse1): Create a MathBigInset when needed

	* src/mathed/math_support.C:
	(deco_table): add lbrace and rbrace

        * src/mathed/math_nestinset.C
        (MathNestInset::interpret): combine the previous math atom with the
        new character to a MathBigInset if possible

        * src/ParagraphParameters.C
        (findToken): move from here

        * src/support/lstrings.[Ch]
        (findToken): to here

        * lib/symbols: add MathBigInset symbols

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@13700 a592a061-630c-0410-9148-cb99ea01b6c8